The present invention relates to an improved process for the preparation of substituted pyrimidines.
Pyrimidines, which are substituted in the 4-position by a hydrocarbyloxy or hydrocarbylthio group are of great commercial interest as highly effective pesticides or pharmaceuticals. U.S. Pat. No. 3,498,984 discloses 2-phenyl4-thiopyrimidines with interesting pharmaceutical properties. U.S. Pat. No. 5,824,624 describes herbicidal compositions comprising 2-phenyl-4-oxypyrimidines. The International Patent Applications WO 98/40379 and WO 98/56789 disclose herbicidal 4-oxypyrimidines, in which a 5-membered heteroaromatic group is attached to the 2-position of the pyrimidine moiety.
These compounds can be prepared for example in a multi-step process including the steps of treating a benzamidine hydrochloride with a substituted acetylacetate in the presence of a strong base to form a 2-phenylpyrimid-4-one, which is subsequently treated with a halogenating agent, in particular a phosphoryl halide to yield a 4-halo-2-phenylpyrimidine, which is reacted with an alcohol or a thioalcohol.
However, this process cannot be used for manufacture of relatively large quantities on an industrial scale due to the high risk of uncontrollable heat generation during the aqueous work up of the halogenation step.
W. Schroth et al., disclose the preparation of 1,3-thiazin-6-thiones by condensation of 3,3-dichloroacrolein and thioamides in the presence of trifluoroborane.
However, there is no motivation to apply this reaction on the manufacture of substituted pyrimidines, especially, since trifluoroborane is not applicable in large scale productions.